Electric control system



n v o lu w H 02 r 1L to o w A? 11 2, vw A km? .5 a H 1-1. 5 cam-2 ELECTRIC CONTROL SYSTEM Filed MarchiZ, 1950 July 17, 1951 Patented July 17, 1951 ELECTRIC CONTROL SYSTEM Harold S. Ogden, Erie, Pa., assignor to General Electric Company, a corporation of New York Application March 2, 1950, Serial No. 147,226

My invention relates to electric power control systems for alternating current dynamo electric machines, and has particular significance in connection with control equipments for series type A.-C. commutator motors such as those used in all-electric traction vehicles.

Heretofore, it has been known to have reduced current starting for alternating current motors but, especially in traction motor control, this is almost universally accomplished by connecting the motor leads across higher and higher voltage taps on a transformer as the motor comes up to speed. This requires great multiplicity of taps and tap changing contactors (each with suitable arc chutes, blow out coils and the like) and some sort of a switching element such as the well-known preventive coil which is expensive, of heavy weight and requires considerable maintenance in the form of periodic dipping and baking.

It is an object of the present invention to provide simple and inexpensive means for overcoming the above mentioned difficulties.

A further object of the present invention is to provide for a relatively great number of starting steps in a motor startin control system utilizing a relatively small number of circuit changing elements.

In the illustrated embodiment the means employed, in the furtherance of these and other objects, comprises for an alternating current traction vehicle equipment including series A.-C. commutator motors; means for providing electrical power through a transformer secondary havin only two changeable taps and sequentially through two ends of a resistance bank adapted to be progressively shorted out to provide a maximum number of accelerating steps with a minimum number of cam operated resistance shorting contacts.

Further objects and advantages will become apparent and my invention will be better understood from consideration of the following description taken in connection with the accompanying single figure of the drawing which is a simplified schematic diagram of power and control circuits for a trolley powered traction vehicle adapted to be propelled by A.-C. commutator type series motors.

In the drawing ll) represents a pantograph adapted to receive power from a traction vehicle such as from a third rail or overhead trolley. Pantograph l and a ground return circuit indicated at H are connected in series with the primary winding I2 of an alternating cur- 3 Claims. (Cl. 323-435) rent transformer having a secondary windin l3. This secondary Winding has an intermediate voltage (e. g., 240 volts) tap M, a full voltage (e. g. 385 volts) tap l5, and a common return point 16. An accelerating resistor bank I l is provided with one end thereof connected to the mid tap M through a normally closed switch contact l8 and the other end connected through a normally open contact IE to the full voltage tap l5. Contacts l8 and I9 operate responsive to energization of a contactor coil 20 as hereinafter explained and it may be found advantae geous to have contacts 18 and I9 each arranged to be time delay opening. Alternatively contacts i8 and I9 may be arranged to operate independently of one another so that both may be opened simultaneously as when clearing short circuits. The resistance bank I! is arranged to be progressively shorted out by a set or ladder of contact units, numbered [-5 inclusive, which may be mounted on a common frame and me--' chanically interlocked one with the other to insure proper sequence of operation. Contacts l-5 are pilot motor-driven cam-operated and the cam development is shown on the drawing for the position i-5 (pilot motor forward), the reversing position R, and positions 5-2 (for reverse operation). In conventional manner, the cam operated contacts may be driven by an air or electric motor and for this purpose I have shown a direct current pilot motor having an armature 2i and field winding 22 adapted to be energized from a source of control power such as a battery 23 through a hand operated master switch 24. The present invention concerns mainly the arrangement of power circuits and the control circuits illustrated, particularly those for energizin the pilot motor (2!- 22), are only incidental, but for the purpose of clarity the control circuits are shown as including a plurality of contacts 2548, inclusive, for reversing the connections to the pilot motor field exciting winding 22 whenever the contactor coil 20 is energized, and the set of motor driven cam operated contacts includes an interlock contact 29 connected in circuit from the source of control power to the contactor coil 20 and acting as a limit switch to cause the pilot motor to reverse whenever the position R is reached as indicated on the cam development. An additional cam operated interlock contact 3!) acts through relay interlock 20a to energize coil 20 and hold the relay in (so that the pilot motor operates in a reverse direction) until position 1 is reached when it drops out ready for, the next start.

Suitable provision may also be provided (as shown through supervisory switch 24) to assure that the control will return to position 1 whenever the control handle is turned to off The resistor bank power circuit cam operated contact arrangement already described is ar ranged in series with two vehicle driving motors each having an armature SI and a field winding 32. If the vehicle is a locomotive, the number of motors used will probably be greater than two but the particular arrangement thereof (such as with suitable reversing switches and possibly with suitable provision for transition from series to parallel operation) is all purely conventional, and forms no part of the present invention.

It is conventional to provide time delay or, al ternatively, current limiting means for controlling the progression of pilot motor driven cam operated controllers in electric traction applications and I have shown a current limit relay having an A. C. coil 33 connected to be energized responsive to voltage drop across a portion of the traction motor loop circuit. In the drawing, coil 33 is shown connected to a shunt 34 in this circuit (though it could just as well be connected across one or both of the series fields 32). The current limit relay has a normally closed contact 35 which opens at some pre determined high value of main motor armature current to interrupt energization of the pilot motor armature and then closes to permit the controller to advance when the motor current falls below this predetermined value.

As an additional feature, I have shown a line contactor having a coil 36 and a normally open contact 31 arranged in the main motor loop circult (near the common return I6 of the transformer secondary). Coil 3B is energized and the line contactor contact 3-? is closed only when the master controller 124 is on on, so that whenever controller 24 is moved to the off position, the positions of tap switches I'I and I8 becomes immaterial and the control is free (without affecting the power circuits) to return to the number 1 position (with only contact unit No. 1 and tap switch I8 closed).

In operation, the pilot motor starts from the first position, (for the first notch in accelerating the car) with cam contact I closed. and the tap switch It closed as indicated by the development in which X indicates that the associated tap contactor is closed and indicates that it is open. For the second step, contact unit number 2 closes cutting out the first section of resistance I'I after which contact number I opens. This sequence of operation continues until contact unit number closes and contact number 4 opens at which time the car is operating on the full 240 volts of the tap I4. If it is desired to continue the acceleration, tap switch I9 closes connecting the resistor across the transformer secondary from tap I4 to tap I5 (assuming I8 is time delay opening). This step in the acceleration is then followed by tap contactor I 8 opening and the traction motor is fed through the resistance bank from tap I5. At this same time, the pilot motor field. circuit is reversed and the cams will go back to the beginning position progressively closing contact units 4, 3, 2 and finally I at which time the traction motors receive full voltage from the 385 volt tap l5 of the transformer. If desired, the system may be so de signed that the ohms resistance from tap switch I8 to tap switch I9 will permit just the right 4 amount of current to fiow so that when tap switch I8 opens the effect is to give the usual tractive effort increment.

All contact units of the motor operated controller may be simple contact units without arc chutes or blow out coils, since as hereinabove fully explained, the sequence of operation is such that the units in the power circuit always close to cut out resistance and are never called upon to open and cut in resistance with the consequent arcing duty which would then be entailed. If desired, any number of cam operated contacts may be used in the power circuits and the use of additional contacts (for example several more than the five shown) will not materially increase the cost of the control.

Power loss in the accelerating resistor is minimized because the acceleration is made in two major steps, that is, first from the tap I4 of the power transformer and then from tap I5 of the power transformer. The system described is simple and will require little maintenance and no expensive preventive coil with the attendant maintenance problems. Neither the tap switches nor the motor operated contacts will be subjected to high surge currents as is the case in conventional alternating current traction motor reduced voltage starting, Furthermore the scheme described is readily adaptable to car equipments which are called upon to operate from either an A.-C. system or a D.-C. system, that is the starting resistance may readily be placed either in circuit with transformer secondary as shown or in circuit with a source of D.-C. supply in case the locomotive or other vehicle is called upon to operate, for example, selectively on 12,000 volts A.-C. outside of and on 600 volts D.-C. within a particular city.

While I have illustrated and described particular embodiments of my invention, modifications thereof will occur to those skilled in the art. I desire it to be understood, therefore, that my invention is not limited to the particular arrangements disclosed, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric control system for an A.-C. motor, said system comprising a transformer having a primary winding and a secondary winding, means for energizing said primary winding, taps from said secondary winding for deriving a plurality of different voltage circuits therefrom, high secondary voltage circuit interrupting means associated with one of said taps, low secondary voltage circuit interrupting means associated with another of said taps, an accelerating resistance having one end thereof connected to said high secondary voltage circuit interrupting means and having the other end thereof connected to said low secondary voltage circuit interrupting means, a ladder of contacts arranged to progressively tap into successive portions of said resistance bank, cam means arranged to sequentially operate the contacts of said ladder, and control means for first connecting the associated end of said resistance through said low secondary voltage circuit interrupting means and operating said cams in one direction and subsequently connecting the opposite end of said resistance bank through said high secondary voltage circuit interrupting means and operating said cams in the opposite directions.

2. An alternating current traction motor power control system comprising a power transformer having a primary winding and a secondary winding, said secondary winding having voltage taps comprising a low voltage tap and a high voltage tap, a common return circuit connection on said transformer secondary win-ding, contact means electrically connected to said low voltage tap, contact means electrically connected to said high voltage tap, a starting resistor having one end thereof adapted to be connected through said first contact means to said low voltage tap and the opposite end thereof adapted to be connected through said second contact means to said high voltage tap, a plurality of cam operated contacts respectively arranged to tap progressively smaller effective portions of said starting resistor from the end thereof adapted to be connected through said second contact means to the end thereof adapted to be connected through said first contact means, a pilot motor for operating said cam operated contacts, control means for simultaneously causing said motor to operate in one direction and causing said first contact means to remain closed and said second contact means to remain open, control means for thereafter reversing the operation of said pilot motor and opening said first contact means and closing said second contact means at a predetermined limit when the cam operated contact adjacent the low voltage end of said accelerating resistance has operated whereby when the sequence of operation of cam operated contacts is reversed at said predetermined limit said contacts may again tap progressively smaller effective portions of said starting resistor.

3. An electric power control system for series type alternating current commutator motors of a traction vehicle, said system comprising a source of alternating current power supply, a transformer having a primary winding and a secondary winding, with said primary winding connected to said source and said secondary winding having voltage taps comprising a low voltage tap, a high voltage tap, and a common return connection to said transformer secondary winding, solenoid coil operated contact means comprising a contact connected in circuit with said low voltage tap and a contact connected in circuit with said high voltage tap, an accelerating resistance bank having one end thereof adapted to be connected in series with the circuit through said contact connected in circuit with said low voltage tap and having the other end thereof adapted tobe connected in series with the circuit through said normally open contact to said high voltage tap, a ladder of contacts arranged to progressively tap into successive portions of said resistance bank, cam means arranged to sequentially operate said contacts, reversible pilot motor means for driving said cam means, said reversible pilot motor means comprising an electric motor having an armature winding, a field winding, a supervisory controlled battery source of control power for em ergizing said motor windings, field reversing means interposed between said source and said field winding, an additional cam operated contact adapted to be operated by said pilot motor and connected in circuit with said solenoid coil across said battery source of control power for interlocking the operation of said contacts in circuit with said voltage taps with the operation of said ladder of contacts, an additional plurality of interlock contacts adapted to be actuated by energization of said solenoid coil and connected in the reversing circuit of said pilot motor, a limit switch for energizing said solenoid coil when all of said cam operated contacts have been caused to operate by said pilot motor, a holding circuit comprising an additional interlock adapted to be operated by said solenoid coil and comprising an additional limit switch adapted to open at the point of beginning, and additional control means for causing the return of said pilot motor to the point of beginning when said master switch is returned to the off position.

HAROLD S. OGDEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,501,369 Ramondo July 15, 1924 2,112,046 Puller, et al. Mar. 22, 1938 FOREIGN PATENTS Number Country Date 411,092 Great Britain May 22, 1934 

